A continuing problem associated with the brazing of members composed of aluminum and aluminum-base alloys is the presence of a tenacious and thermally stable oxide layer on the surfaces of such members which resists the penetration of the aluminum brazing filler metal, thereby preventing wetting of the base metal and inhibiting flow of the molten filler metal between the surfaces to be joined. While the oxide layer can be satisfactorily removed from the surfaces of such components employing various chemical and mechanical pickling and cleaning techniques, the oxide layer forms almost instantaneously on the cleaned surfaces when exposed to atmospheres containing oxygen even at relatively high vacuum levels. Since the handling of such preliminarily cleaned aluminum components in high vacuum or high purity inert atmospheres is impractical from a commercial standpoint, it has heretofore been proposed to employ various fluxing agents which are effective to dissolve the oxide layer or to etch the metal surface so as to release the oxide in order to facilitate a penetration and wetting of the base metal by the molten brazing filler metal. While the use of such prior art fluxing agents has been found satisfactory in some instances, their use is generally not desirable because of their inherent corrosive nature, necessitating a removal of the residual flux remaining at the completion of the brazing operation by expensive and time-consuming techniques. In some instances, the flux residue is inaccessible due to the nature of the brazed assembly, making it impossible to effectively remove, whereby the brazed component is possessed of properties less than optimum.
In order to overcome the disadvantages associated with the use of prior art brazing fluxes, it has heretofore been proposed to employ a magnesium vapor in the brazing furnace during the brazing operation, whereby penetration of the aluminum oxide film by the brazing filler metal is effected, providing a wetting of the base metal. A method of the foregoing type is disclosed in U.S. Pat. No. 3,378,914. The use of such metallic vapor atmospheres is generally undesirable due to the tendency of the vapors to condense and deposit on cooler portions of the furnace and pumping equipment, causing malfunction and necessitating periodic cleaning of the equipment.
The present invention overcomes many of the problems and disadvantages associated with prior art techniques for brazing aluminum and its alloys, by providing a process which is simple, economical and commercially practical and provides for penetration of the oxide layer, a good degree of wetting of the base metal and a satisfactory flow of the brazing filler metal over a considerable distance along the surfaces of the joint or fracture being brazed.